The projection image display device (projector device) that enlarges and displays an image is widely used for purposes from personal theater to business presentations. An ultrahigh pressure mercury lamp is mainly used as a light source for such a projector device. However, there are problems of a short life of light source, environmental loads imposed by mercury use, and the like. The ultrahigh pressure mercury lamp is not the best light source for projector device that are becoming increasingly miniaturized. This is because optical systems become complex due to the separation of white light into three primary colors and because it is difficult to design a compact optical engine due to large etendue.
To solve these problems, development of a projector device that includes a semiconductor laser as a light source has been pursued. A laser light source has the characteristics of high light use efficiency because of high directionality, low power consumption, and a long life.
Further, there has been offered a method to obtain light that has the required color by causing a phosphor to emit light by using the blue light or the ultraviolet light of the semiconductor laser as excitation light.
Patent Document 1 (JP2010-237443A) offers a configuration where a circular substrate attached to a wheel motor is divided into a region coated with a phosphor for emitting red fluorescent light, a region coated with a phosphor for emitting green fluorescent light, and a region for transmitting blue laser light. With this configuration, by applying excitation light to the specific position of the substrate while rotating the wheel motor, red fluorescent light, green fluorescent light, and blue laser light can be generated in time division to be used as light sources for the projector device. Further, the configuration simultaneously provides the effect of preventing thermal damage to the phosphor by rotating the substrate coated with the phosphor by the wheel motor to disperse the energy of excitation laser condensed on the phosphor. Such a hybrid light source combining a semiconductor laser with the phosphor is expected to become the light source of the high-output and compact projector device.
In the projector device that uses the laser light, speckle noise is a problem. As a general method for reducing the speckle noise, there are two approaches, namely, incoherent conversion of the laser light and reduction of apparent speckle noise.
The former is a method for converting the laser light into incoherent light (incoherency) by eliminating coherency of the laser light, which is performed by broadening the wavelength width by high-frequency superimposition, multiplexing laser light having a delay longer than a coherent distance, or superimposing orthogonal polarized lights. This method is essentially designed to prevent generation of speckles by changing the nature of light itself. Thus, the semiconductor laser itself or a driving circuit must be directly revised, or the optical system must be greatly changed. In many cases, the method is compositely combined with other methods to be used because it is difficult to obtain satisfactory effects alone.
The latter is a method for reducing apparent speckle noise by superimposing the speckle patterns of an image a plurality of times to integrate them within time (less than 20 ms) where the patterns are discernible to the human eye, and then by averaging speckle noise to a level to be ignored by the human eyes, which is performed by swinging the screen or vibrating an optical component. This method does not essentially change the nature of light. Accordingly, though generated, speckles cannot be recognized by the human eyes due to optical illusion. With this method, effects are conspicuous due to optical illusion. However, the screen swinging is applied only to a part of a rear projectors or the like because it necessitates a big structure and imposes restrictions on the screen.
Patent Document 2 (JP11-064789A) discloses a method for reducing speckle noise by causing an optical component to vibrate. FIGS. 1a-1b are perspective views schematically showing a configuration for reducing speckle noise: FIG. 1a showing a first related art, and FIG. 1b showing a second related art. In the general projector device, laser light from laser light source 2 is converted into parallel light by collimator lens 3, and transmitted through various optical components including light integrator 9b, a condenser lens 12a, or the like to enter into spatial light modulation element 10a. Then, light modulation is performed at spatial light modulation element 10a according to an image signal, and subsequently enlarged and projected to a screen (not shown). With this configuration, in the first related art shown in FIG. 1a, by rotating light integrator 9b including a pair of fly-eye lenses 16c and 16d located between a combination of laser light source 2 with collimator lens 3 and a combination of condenser lens 12a with spatial light modulation element 10a, around the optical axis, the speckle pattern is temporally and spatially moved in the optical system, and speckles formed on the retina are integrated, thereby reducing apparent speckle noise. In the second related art shown in FIG. 1b, by rotating light integrator 9c including rod lens 26a (transparent medium such as glass having rectangular surface) located between a combination of laser light source 2, collimator lens 3, and condenser lens 27a and a combination of condenser lens 12a with spatial light modulation element 10a, around the optical axis, similar effects are obtained.
FIGS. 2a-2b are schematic plan views showing another configuration for reducing speckle noise: FIG. 2a showing a third related art, and FIG. 2b showing a fourth related art. The third and fourth related arts are disclosed in Patent Document 3 (JP7-297111A). In the third related art shown in FIG. 2a, condenser lens 27b and collector lens 29a are arranged on the optical path of laser light, and a dynamic scattering medium (diffusion plate 20f) that is driven by motor 28 to rotate is disposed therebetween. In the fourth related art shown in FIG. 2b, a dynamic scattering medium (diffusion plate 20g) driven by signal source 31 and transducer 30 to vibrate ultrasonically is disposed on an optical path between condenser lens 27c including mirror part 32 and collector lens 29b. With this configuration, a scattering state on the optical path is changed by diffusion plates 20f and 20g to cause the speckle pattern to vibrate temporally and spatially, and speckles formed on the retina are integrated, thereby reducing apparent speckle noise.
FIGS. 3a-3b are schematic plan views showing yet another configuration for reducing speckle noise: FIG. 3a showing a fifth related art, and FIG. 3b showing a sixth related art. The fifth and sixth related arts are disclosed in Patent Document 4 (JP2003-098476A).
In the fifth related art shown in FIG. 3a, diffusion plate 20h is disposed between beam expansion optics 33 including a magnifying lens (collimator lens 3e) and collimator lens 3f and beam forming optics 34 including a pair of fly-eye lenses 16e and 16f and condenser lenses 12c and 12d. Diffusion plate 20h is swung by motion application means 35a. Accordingly, the speckle pattern is vibrated temporally and spatially, and speckles formed on the retina are integrated, thereby reducing apparent speckle noise. On the downstream side of beam forming optics 34, a pair of polarization plates 37 and 38 and polarized beam splitter 36 located therebetween are arranged.
In the sixth related art shown in FIG. 3b, in addition to the aforementioned configuration, diffusion plate 20i is disposed between beam forming optics 34 and spatial light modulation element 10d, and swung by motion application means 35b. By swinging two diffusion plates 20h and 20i by motion application means 35a and 35b, the effect of reducing the speckle noise is improved. Motion application means 35a and 35b can be made common.
FIGS. 4a-4b are schematic plan views showing yet another configuration for reducing speckle noise: FIG. 4a showing a seventh related art, and FIG. 4b showing an eighth related art. The seventh and eighth related arts are disclosed in Patent Document 5 (WO2005/008330A1). In the seventh related art shown in FIG. 4a, as in the case of the aforementioned fifth and sixth related arts, diffusion plate 20j is disposed in the midway of the optical path (in this case, incident side position of spatial light modulation element 10a). Diffusion plate 20j is connected to diffusion plate swinging part 39. Speckle noise is effectively reduced by setting swinging speed V of diffusion plate 20j to V>d×30 with respect to particle size d of diffusion plate 20j. Further, the diffusion angle of diffusion plate 20j is set to be limited with respect to the numerical aperture of an illumination optical system and the brightness of a projection lens. Thus, the light amount loss of laser light by diffusion plate 20j is reduced. In the eighth related art shown in FIG. 4b, a configuration including rod lens 26b as a light integrator in place of the pair of fly-eye lenses 16e and 16f is disclosed.
Because the light condensation of the laser light is high because it has a single wavelength, and light intensity has the gaussian distribution (single mode), so that a local energy density during light condensing is extremely high. Accordingly, when excitation laser light 17a is condensed on phosphor 6, phosphor 6 easily receives thermal damage. In such a case, no fluorescent light is generated, which causes the color of the projected image to deteriorate. When the thermal damage further progresses, circular substrate 7 coated with phosphor 6 is damaged, excitation laser light 17a travels through circular substrate 7, which increases the possibility that a safety problem will occur.
To prevent this, during the operation of projector device 1, circular substrate 7 coated with phosphor 6 is connected to wheel motor 8 to be rotated, and the energy of excitation laser light 17a condensed on phosphor 6 is dispersed, thereby preventing thermal damage to the specific part of phosphor 6.